There seems to be a duplicate of this post. In case you didn't see an answer in the other one it is below: (I'll keep an eye on them and delete one of them later.)

Quote Originally Posted by 3dkarma View Post
Two options I'm aware of:

XTC3D - a coating you paint on http://www.reynoldsam.com/product/xt...campaign=XTC3D
Vapour smoothing with THF (similar process to smoothing ABS with acetone) http://www.protoparadigm.com/news-up...ydrofuran-thf/